1. Field of the Invention
This invention relates to the chemical arts. In particular, it relates to a method for isolating and radiolabeling leukocytes for subsequent in vivo use.
2. Description of the Related Art
A source of substantially pure leukocytes, i.e., leukocytes free from platelets, red blood cells and/or other components of whole blood, is important in a number of applications. One particularly significant application is to provide leukocytes for labeling with radioactive markers, such as technetium-99m and indium-111. The radiolabeled leukocytes are then used in a variety of diagnostic methods, including administration back into the human from whom the leukocytes were originally obtained. After the radiolabeled leukocytes have accumulated in the area to be imaged, they can be detected by scintigraphic techniques.
Several relatively simple methods, such as sedimentation and centrifugation, are known for separating leukocytes from red blood cells and/or other components of whole blood. Unfortunately, the leukocyte fraction obtained by such basic techniques contains platelets that can make the fraction unsuitable in certain applications, such as scintigraphy. Contamination of radiolabeled leukocytes by radiolabeled platelets, red blood cells and/or other components of whole blood is undesirable, because it exposes the patient to a higher than necessary dosage of the radioactive marker.
Accordingly, it is a desideratum for a method for isolating substantially pure leukocytes. Such a method must be relatively quick, simple and inexpensive, so that it can be easily employed by hospital and laboratory technologists.
Further, it is a desideratum for a method that produces substantially pure leukocytes without damaging the viability of the cells or leaving trace residues of reagents or other byproducts that would prevent the cells from being administered into a patient. For example, it is known that the effectiveness of centrifugation can be enhanced by using a discontinuous density gradient. With discontinuous density gradient centrifugation, an aqueous suspension of blood cells is layered over or underlayered a concentrated aqueous solution containing a nonreactive solute, such as a Ficoll-Hypaque mixture. The cells and gradients are then centrifuged at a rate sufficient to cause the cells to settle faster than they would under normal gravity. The spinning continues until the leukocytes collect at the gradient boundary. It is a disadvantage of discontinuous density centrifugation, however, that the nonreactive solutes, such as the Ficoll-Hypaque mixture, are not approved for use in humans. Therefore, the leukocytes isolated by this method cannot be used in vivo.
Once the substantially pure leukocytes have been isolated, there remains a further need for a simple and reproducible procedure for labeling the leukocytes with an effective and safe amount of a radioactive marker. If too little marker is incorporated, it may be impossible to detect the radiolabeled leukocytes once they have been reintroduced back into the patient. However, if too much marker is incorporated, the patient may be exposed to a higher than necessary dosage of the radioactive marker. Therefore, it is a further desideratum for an effective method for labeling substantially pure leukocytes with a suitable amount of a radioactive marker.
Accordingly, there has existed a definite need for a relatively quick, simple, and inexpensive method to isolate substantially pure leukocytes. There has existed a further need for a method to isolate substantially pure leukocytes for in vivo use. There has existed a still further need for a method to label the substantially pure leukocytes with an effective and safe amount of a radioactive marker. The present invention satisfies these and other needs and provides further related advantages.